Press Alt + R to read the document text or Alt + P to download or print.
This document contains no pages.
HomeMy WebLinkAbout15 Stormwater Report Updated 8-21-20 2131 GRAF
MASTER SITE PLAN
LOT 2, MINOR SUB. 235
STORMWATER DESIGN REPORT
A. Introduction
This design report will give an overview of the proposed stormwater system for the 26-acre Graf
Street Apartments Master Site Plan located in Lot 2 of Minor Sub. 235, Section 23, T02 S., R05
E., Bozeman, Montana.
The project site is broken into two phases of development. Phase 1 includes the extension of
Lantern Drive, South 21st Avenue, required parkland, and development of the northern half of
the net lot areas. Phase 2 will consist of the development of the southern half of the net lot areas.
The proposed storm water management system consists of overland sheet flow, curb and gutter,
sidewalk chases, and swales to direct runoff towards either permeable paver infiltration systems
and gravel infiltration systems for on-site development, or underground retention chambers for S
21st Ave. Lantern Drive was not included in this report, because it was previously accounted for
in the Nexus Point stormwater design report. Nexus Point is the adjacent project to the north,
which will be constructed prior to this project.
The following references were used in the preparation of this report:
a. COB Design Standards and Specifications Policy, 2004. Addendum #7
b. COB Modifications to Montana Public Works Standard Specifications (MPWSS)
The delineated basins, drainage plans, grading plans, and details are displayed on the sheets in
Appendix A.
B. Runoff and Basin Estimates
25-year storm event runoff rates were calculated for the pertinent basins utilizing the rational
method in accordance with the COB design standards. A runoff coefficient C of 0.71 was
determined for the total developable area of the site. The total developable area includes the net
lot areas, roadway and trail easements, but excludes the areas of Lantern Park and the
watercourse setbacks.
Area C
Total Area 897,198 NA
Impervious 657626 0.9
Landscaped 239572 0.2
Weighted C NA 0.71
Basins 9 and 10 are the basins of concern for conveyance sizing as they are the basins for S 21st
Ave. Runoff from these basins is conveyed via curb and gutter to two curb inlets, and is then
piped to underground retention chambers. The 25-year flow rates for basins 9 & 10 are 2.0 cfs
and 1.9 cfs respectively, calculations are included in Appendix B.
C. Conveyance Capacity
The proposed infrastructure improvements were designed to convey runoff per the City of
Bozeman standards. The conveyance structures include concrete curb-gutter and storm drain
piping. The curb & gutter capacity at the minimum project slope of 1% without overtopping a
depth of 0.15’ below the top of the curb is 4.04 cfs, exceeding the peak runoffs. Runoff from
Basins 9 & 10 enters storm drain curb inlets and is then piped to underground retention
chambers. The storm drain piping was sized to be 15” diameter PVC. Calculations are included
in Appendix B.
Lantern Drive was not included in this report, because it was previously accounted for in the
Nexus Point stormwater design report. The previous report indicated that 15” diameter PVC
would be sufficient for the Lantern Drive inlets.
D. Inlet Grate Sizing
The curb inlet that receives runoff from drainage basins 9 and 10 were checked for capacity. The
selected inlet has a capacity of 2.51 cfs. This exceeds the maximum 25-year storm runoff
tributary to that point of 2.0 cfs. Calculations are included in Appendix B.
The selected nyloplast 8” area drains have a capacity of 0.32 cfs at the design head of 0.25’.
Basin 7 has an estimated 25-year peak runoff of 2.5 cfs, which would require 8 inlet drains.
Adequate area inlets have been provided to meet the incoming peak runoff. The manufacturer’s
flow rate information is included in Appendix B.
E. Native Gravel Infiltration Rates
The infiltration rate of native gravels was determined using a constant-head test. Two test pits
were utilized for testing (TP-01 and TP-51). See Appendix C for a test pit location map. Each
test pit was pre-soaked with approximately 60 gallons of water before testing. The pre-soak
period was completed to simulate a saturated ground condition prior to performing the constant-
head test. Two tests were completed at each test pit. The average infiltration rate was found to
be 2.76 inches per minute. Providing a factor of safety of 2, the design of the pervious pavers
used an infiltration rate of 1.38 inches per minute. The infiltration rate of the native gravels is
much less than that of the block pavers, so the native gravels control. See Appendix C for
infiltration rate calculations.
F. Stormwater Detention/Retention Volumes and Infiltration System Calculations
All of the Runoff is proposed to be conveyed to underground storage systems and ultimately
infiltrate into native gravels. Three types of underground systems are proposed: pervious pavers,
area drain inlets with perforated pipe wrapped in drain rock, and Contech retention chambers.
Groundwater monitoring was conducted to determine the seasonal high groundwater levels.
Groundwater monitoring data is included in Appendix D. The groundwater depth below existing
grade is summarized in the table below:
Groundwater Depth Below Existing Grade (ft)
Date Well 1 Well 2 Well 3 Well 4
5/8/2020 5.37 0.00 0.00 6.49
5/15/2020 5.57 5.65 4.65 6.58
5/27/2020 5.94 5.75 4.67 6.68
6/5/2020 5.73 6.00 4.85 6.64
6/12/2020 4.54 5.98 4.80 6.45
6/19/2020 4.17 5.93 4.62 6.22
6/26/2020 4.64 5.89 4.64 6.41
7/3/2020 4.55 6.00 4.58 6.30
7/13/2020 5.81 6.11 4.89 6.62
7/20/2020 4.76 5.32 4.64 6.56
7/27/2020 4.52 5.56 4.77 6.52
Min 4.17 5.32 4.58 6.22
Max 5.94 6.11 4.89 6.68
The seasonal groundwater data was then utilized to model the seasonal high groundwater
surface. The surface was used to approximate the seasonal high groundwater level at the
location of all the buried storage and infiltration facilities. The bottom of the storage elevation
was then set to be above the seasonal high groundwater. The storage areas and volumes were
sized based on the depth to groundwater. Figures 1 and 2 of the geotechnical report, which are
included in Appendix D, were used to approximate the depth of native gravel. The proposed
storage systems, bottom of retention storage elevations, seasonal high groundwater elevations,
approximate depths to gravel, and approximate native gravel elevations are summarized in the
following table, additional information is included in Appendix E:
Groundwater Surface & Gravel Depth Summary
Location
Bottom
of
Retention
Storage
Elevation
(ft)
Seasonal
High
Groundwater
Surface
Elevation
(ft)
Nearest
Test Pit
*Figure
1 of
Geotech
Approximate
Depth to
Gravel (ft)
*Figure 2 of
Geotech
Estimated
Native
Gravel
Elevation
(ft)
Basin 1 Pervious Pavers 4961.68 4961.25 TP-17 3.8 4962.2
Basin 2 Pervious Pavers 4964.26 4961 TP-18 5.1 4963.4
Basin 3 Pervious Pavers 4964.77 4964.5 TP-52 1.9 4968.1
Basin 4 Pervious Pavers 4967.74 4967.5 TP-49 1.5 4970.5
Basin 5 Pervious Pavers 4970.24 4967.75 TP-11 3.0 4972
Basin 6 Pervious Pavers 4969.34 4969 TP-43 3.7 4970.3
Basin 7 Infiltration System 4961 4961 TP-01 2.9 4961.1
Basin 8 Pervious Pavers 4972.5 4968 TP-27 3.2 4973.8
Basin 9 & 10 Retention Chambers 4963 4962.5 TP-34 4.0 4965
Basin 11 Infiltration System 4963 4960 TP-17 3.8 4960.2
The detention and retention storage volumes were sized based on the depth to high groundwater
and on a 10 year 2 hour event per the City Design Standards. Detention systems were sized to
include infiltration rates. The Retention system serving the public street, S 21st Ave, was sized to
totally retain the 10 year 2 hour storm per the City Engineering Department’s request. The City
did not want to include infiltration in the equations for the public street Retention System. The
calculations for all stormwater storage facilities are included in Appendix E.
The proposed stormwater facilities reduce the Post-development runoff rate to zero. All runoff is
conveyed to the infiltration retention and detention systems and then infiltrates into the ground.
In the event that a storm greater than the design storm occurs, emergency overflows route runoff
onto street drainage systems, minimizing damage to buildings or structures.
G. Stormwater Facility Maintenance
The proposed storm drainage facilities will be privately operated and maintained by the property
owners association of the on-site development. The POA covenants should include provisions
for storm water maintenance included in Appendix E.
Appendices
A. Drawings and Details
B. Runoff, Conveyance, and Inlet Calculations
C. Test Pit Location Map and Infiltration Calculations
D. Groundwater Monitoring Data and Geotech Report Figures
E. Detention and Retention Calculations
F. Stormwater Maintenance Plan
Appendices
Appendix A – Drawings and Details
PUBLIC PARK
BLDG 4
TYPE B
2171 GRAF ST
BLDG 2
TYPE C
2161 GRAF
ST
BLDG 6
TYPE B
2179 GRAF ST
BLDG
5
TYPE
A
2175
GRAF
ST
BLDG 19
TYPE B
2141 GRAF ST
BLDG 16
TYPE C
2155 GRAF
ST
BLDG 17
CLUB
HOUSE
2131
GRAF ST
BLDG 3
TYPE D
2171
GRAF
BLDG 10
TYPE B
2065 GRAF ST
BLDG 13
TYPE C
2051 GRAF ST
BLD
G
1
5
T
Y
P
E
A
2061
G
R
A
F
S
T
BLDG 21
TYPE B
2151 GRAF ST
BLDG 18
TYPE C
2135 GRAF ST
BLDG 20
TYPE B
2145 GRAF ST
BLDG 12
TYPE C
2069 GRAF ST
BLDG 7
TYPE B
2181 GRAF ST
BLDG 1
TYPE E
CLUB
HOUSE
2079
GRAF ST
BLDG 8
TYPE B
2071 GRAF ST
BLDG 9
TYPE B
2075
GRAF ST
BLDG 11 TYPE A
2067 GRAF ST
BASIN 11
22915 SF
BASIN 5
183041 SF
BASIN 10
63983 SF
BASIN 9
66769 SF
BASIN 3
51818 SF
BASIN 6
126106 SF
LANTERN DRIVE
S
2
1
S
T
A
V
E
S
2
1
S
T
A
V
E
WEST GRAF ST
S
1
9
T
H
A
V
E
BASIN 1
160623 SF
BASIN 7
82565 SF
BASIN 2
15581 SF
BASIN 4
48789 SF
BASIN 8
17555 SF
1" =
0
SCALE
70
1403570
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
,
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
(
4
0
6
)
5
8
6
-
5
7
4
0
F
A
X
2131 GRAF
STORM DRAIN
SD1.1
21
3
1
G
R
A
F
ST
O
R
M
D
R
A
I
N
A
G
E
B
A
S
I
N
E
X
H
I
B
I
T
LEGEND
BO
Z
E
M
A
N
,
M
T
PUBLIC PARK
BLDG 4
TYPE B
2171 GRAF ST
BLDG 2
TYPE C
2161 GRAF
ST
BLDG 6
TYPE B
2179 GRAF ST
BLDG
5
TYPE
A
2175
GRAF
ST
BLDG 19
TYPE B
2141 GRAF ST
BLDG 16
TYPE C
2155 GRAF
ST
BLDG 17
CLUB
HOUSE
2131
GRAF ST
BLDG 3
TYPE D
2171
GRAF
BLDG 10
TYPE B
2065 GRAF ST
BLDG 13
TYPE C
2051 GRAF ST
BLD
G
1
5
T
Y
P
E
A
206
1
G
R
A
F
S
T
BLDG 21
TYPE B
2151 GRAF ST
BLDG 18
TYPE C
2135 GRAF ST
BLDG 20
TYPE B
2145 GRAF ST
BLDG 12
TYPE C
2069 GRAF ST
BLDG 7
TYPE B
2181 GRAF ST
BLDG 1
TYPE E
CLUB
HOUSE
2079
GRAF ST
BLDG 8
TYPE B
2071 GRAF ST
BLDG 9
TYPE B
2075
GRAF ST
BLDG 11 TYPE A
2067 GRAF ST
F.F.
ELEV
4973.0
F.F. ELEV
4968.0
F.F. ELEV
4974.9
F.F.
ELEV
4969.6
F.F.
ELEV
4968.1
F.F. ELEV
4970.9
F.F. ELEV
4977.4±
F.F. ELEV
4972.6
F.F. ELEV
4975.0
F.F. ELEV
4977.3
F.F. ELEV
4983.0
F.F. ELEV
4977.50±
F.F. ELEV
4973.00
F.F. ELEV
4978.8±F.F.
ELEV
4977.0±
F.F. ELEV
4982.0±
F.F. ELEV
4979.5±
F.F. ELEV
4982.5±
F.F. ELEV
4978.2±
F.F.
E
L
E
V
4978
.
5
±
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
1 inch =
0
SCALE
50'
100'25'50'
2131 GRAF
GRADING PLAN
C0.5
GRAF STREET
S
1
9
T
H
AV
E
N
U
E
PROPOSED
PUBLIC PARK
LANTERN DR
OV
E
R
A
L
L
G
R
A
D
I
N
G
P
L
A
N
21
3
1
G
R
A
F
BO
Z
E
M
A
N
,
M
T
LEGEND
PHASE I
EAST
PHASE I
WEST
FUTURE
PHASE
WEST
FUTURE
PHASE
EAST
SO
U
T
H
2
1
S
T
A
V
E
N
U
E
PUBLIC PARK
BLDG 4
TYPE B
2171 GRAF ST
BLDG 2
TYPE C
2161 GRAF
ST
BLDG 6
TYPE B
2179 GRAF ST
BLDG
5
TYPE
A
2175
GRAF
ST
BLDG 3
TYPE D
2171
GRAF
BLDG 7
TYPE B
2181 GRAF ST
BLDG 1
TYPE E
CLUB
HOUSE
2079
GRAF ST
BLDG 8
TYPE B
2071 GRAF ST
BLDG 9
TYPE B
2075
GRAF ST
LANTERN DRIVE (CONSTRUCTED WITH NEXUS POINT)
S
2
1
S
T
A
V
E
S
2
1
S
T
A
V
E
1" =
0
SCALE
40
802040
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
,
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
(
4
0
6
)
5
8
6
-
5
7
4
0
F
A
X
2131 GRAF
DRAINAGE PLAN
C1.5
21
3
1
G
R
A
F
PH
A
S
E
1
D
R
A
I
N
A
G
E
P
L
A
N
LEGEND
BO
Z
E
M
A
N
,
M
T
BLDG 6
TYPE B
2179 GRAF ST
BLDG 19
TYPE B
2141 GRAF ST
BLDG 16
TYPE C
2155 GRAF
ST
BLDG 17
CLUB
HOUSE
2131
GRAF ST
BLDG 10
TYPE B
2065 GRAF ST
BLDG 13
TYPE C
2051 GRAF ST
BLD
G
1
5
T
Y
P
E
A
206
1
G
R
A
F
S
T
BLDG 21
TYPE B
2151 GRAF ST
BLDG 18
TYPE C
2135 GRAF ST
BLDG 20
TYPE B
2145 GRAF ST
BLDG 12
TYPE C
2069 GRAF ST
BLDG 7
TYPE B
2181 GRAF ST
BLDG 8
TYPE B
2071 GRAF ST
GRAF ST
BLDG 11 TYPE A
2067 GRAF ST
FUTURE PHASE FUTURE PHASE
S
2
1
S
T
A
V
E
WEST GRAF ST
1" =
0
SCALE
40
802040
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
,
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
(
4
0
6
)
5
8
6
-
5
7
4
0
F
A
X
2131 GRAF
DRAINAGE PLAN
C1.6
21
3
1
G
R
A
F
FU
T
U
R
E
P
H
A
S
E
D
R
A
I
N
A
G
E
P
L
A
N
LEGEND
BO
Z
E
M
A
N
,
M
T
BLDG 4
TYPE B
2171 GRAF ST
BLDG 2
TYPE C
2161 GRAF
ST
BLDG 6
TYPE B
2179 GRAF ST
BLDG
5
TYPE
A
2175
GRAF
ST
BLDG 3
TYPE D
2171
GRAF
BLDG 7
TYPE B
2181 GRAF ST
BLDG 1
TYPE E
CLUB
HOUSE
2079
GRAF ST
1 inch =
0
SCALE
30'
60'15'30'
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
2131 GRAF
GRADING PLAN
C1.7
GR
A
D
I
N
G
P
L
A
N
-
P
H
A
S
E
I
E
A
S
T
21
3
1
G
R
A
F
BO
Z
E
M
A
N
,
M
T
LANTERN DRIVE CONSTRUCTED WITH NEXUS POINT
FUTURE
PHASE
PHASE
I EAST
SEE
SHT
C1.8
SO
U
T
H
2
1
S
T
AV
E
N
U
E
PHASE
LINE
FUTURE
PHASE
LEGEND
PUBLIC PARK
BLDG 2
TYPE C
2161 GRAF
BLDG 1
TYPE E
CLUB
HOUSE
2079
GRAF ST
BLDG 8
TYPE B
2071 GRAF ST
BLDG 9
TYPE B
2075
GRAF ST
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
1 inch =
0
SCALE
30'
60'15'30'
2131 GRAF
GRADING PLAN
C1.8
GR
A
D
I
N
G
P
L
A
N
-
P
H
A
S
E
I
W
E
S
T
21
3
1
G
R
A
F
BO
Z
E
M
A
N
,
M
T
SO
U
T
H
1
9
T
H
A
V
E
N
U
E
LANTERN
DRIVE
SO
U
T
H
2
1
S
T
AV
E
N
U
E
LEGEND
FUTURE
PHASE
PHASE
I WEST
SEE
SHT
C1.7
PHASE
LINE
DETAIL1
C2.2 CMP ROUND PERFORATED PIPE - RETENTION/INFILTRATION SYSTEM
DETAIL3
C2.2 CONCRETE VALLEY GUTTER DETAIL4
C2.2 CURB CHASE
DETAIL2
C2.2 PERVIOUS PAVER DETAIL
DETAIL5
C2.2 GRAVEL INFILTRATION SYSTEM
DETAIL6
C2.2 PARK PLAYGROUND INFILTRATOR
SHEET
MA
D
I
S
O
N
E
N
G
I
N
E
E
R
I
N
G
89
5
T
E
C
H
N
O
L
O
G
Y
B
L
V
D
S
U
I
T
E
2
0
3
BO
Z
E
M
A
N
,
M
T
5
9
7
1
8
(4
0
6
)
5
8
6
-
0
2
6
2
(
4
0
6
)
5
8
6
-
5
7
4
0
F
A
X
2131 GRAF
CIVIL DETAILS
C2.2
21
3
1
G
R
A
F
CI
V
I
L
D
E
T
A
I
L
S
BO
Z
E
M
A
N
,
M
T
11.75"
13.7"END VIEWTOP VIEW
T
O
P
V
I
E
W
I
N
T
E
R
C
O
N
N
E
C
T
E
D
B
L
O
C
K
S
4.5"1"10"R
0
.
2
5
"
4"
1
0
.
2
5
"
D
R
A
I
N
A
G
E
S
P
A
C
E
R
0.5"R0.5"
0
.
2
5
"
4
5
°
1
"
X
1
4
"
A
A
S
I
D
E
V
I
E
W
0
.
2
5
"
O
P
E
N
J
O
I
N
T
(
T
Y
P
)
P
O
W
E
R
B
L
O
C
K
(
S
I
D
E
V
I
E
W
)
6
"
M
I
N
.
*
*
3
4
"
-
1
"
C
L
E
A
N
,
W
A
S
H
E
D
A
N
G
U
L
A
R
S
T
O
N
E
S
E
C
T
I
O
N
A
-
A
V
I
E
W
A
C
F
M
2
0
0
W
O
V
E
N
G
E
O
T
E
X
T
I
L
E
(
O
R
A
S
S
H
O
W
N
O
N
P
L
A
N
S
)
1
4
"
O
P
E
N
J
O
I
N
T
*
S
U
B
G
R
A
D
E
T
O
B
E
P
R
E
P
A
R
E
D
P
E
R
E
N
G
I
N
E
E
R
O
F
R
E
C
O
R
D
'
S
S
P
E
C
I
F
I
C
A
T
I
O
N
S
(
S
E
E
P
L
A
N
S
)
A
C
F
P
O
W
E
R
B
L
O
C
K
O
P
E
N
J
O
I
N
T
P
A
V
E
R
F
O
R
A
D
D
I
T
I
O
N
A
L
I
N
F
O
R
M
A
T
I
O
N
P
L
E
A
S
E
C
O
N
T
A
C
T
:
A
C
F
E
N
V
I
R
O
N
M
E
N
T
A
L
,
1
-
8
0
0
-
4
4
8
-
3
6
3
6
,
w
w
w
.
a
c
f
e
n
v
i
r
o
n
m
e
n
t
a
l
.
c
o
m
0
7
/
0
7
/
1
7
* 14" OPEN JOINTS SHALL BE UNFIL
L
E
D
AND FREE OF STONE/SAND BACK
F
I
L
L
.
** RECOMMENDED STONE BAS
E
D
E
P
T
H
S
DEPTHS LISTED BELOW ARE SU
B
J
E
C
T
T
O
CBR TESTS AND THE DESIGN E
N
G
I
N
E
E
R
'
S
SUBGRADE SUPPORT CALCUL
A
T
I
O
N
S
.
PEDESTRIAN TRAFFIC
6
"
-
8
"
M
I
N
.
PASSENGER VEHICLE TRAFFIC
1
2
"
M
I
N
.
INDUSTRIAL TRAFFIC
1
8
"
M
I
N
.
Appendix B – Runoff, Conveyance, and Inlet
Calculations
Drainage Basin No.Area (Ac.) Weighted C 100 Yr 25 Yr 10 Yr
7 1.895 0.71 4.4 2.5 1.8
9 1.533 0.71 3.5 2.0 1.4
10 1.469 0.71 3.4 1.9 1.4
General Equation:i = a/(b+D)n where D is duration in hours, i = intensity in inches/hour
Design Rainfall Freq.100 25 10
IDF coefficient a 1.01 0.78 0.64
IDF coefficient b 0 0 0
IDF coefficient n 0.67 0.64 0.65
Adjustment Factor Cf:1.25 1.1 1
Area C
Total Area 897,198 NA
Impervious 657,626 0.9
Landscaped 239,572 0.20
Weighted C NA 0.71
Drainage Basin 7
Area 1.90 acres
0.71
1.00 percent
700 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.89 0.78 0.71 (Shall not exceed 1.00)
Total tc:10.51 15.78 19.30 minutes
intensity at tc 3.24 1.83 1.34 in/hr
4.37 2.47 1.80 cfs
Drainage Basin 9
Area 1.53 acres
0.71
1.30 percent
900 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.89 0.78 0.71 (Shall not exceed 1.00)
Total tc:10.72 16.22 19.89 minutes
intensity at tc 3.20 1.80 1.31 in/hr
3.50 1.97 1.43 cfs
Drainage Basin 10
Area 1.47 acres
0.71
1.30 percent
900 feet
Design Rainfall Freq. 100 25 10 years
C*Cf 0.89 0.78 0.71 (Shall not exceed 1.00)
Total tc:10.72 16.22 19.89 minutes
intensity at tc 3.20 1.80 1.31 in/hr
3.35 1.89 1.37 cfs
Runoff Coefficient
Peak Q values
Graf Street Apartments, Lot 2 of Minor Sub. 235
Peak Flow Summary (cfs)
Storm Information
IDF Equations from Bozeman Stormwater Master Plan for City of Bozeman, March 1982
Peak flow calculations
Curb Inlet Drainage Areas - Post Development
See SD1.1 for visual reference
Weighted C
Average slope
peak runoff:
Travel Distance
Weighted C
Average slope
Travel Distance
Weighted C
Average slope
Travel Distance
peak runoff:
peak runoff:
Allowable Pavement Encroachment
Given: T =9 feet (max per city)
W =1.5 feet
Ts =7.5 feet
Sw =0.0625 ft/ft
Sx =0.03 ft/ft
a =0.59 inches
d =3.24 inches
n =0.015
Sw/Sx =2.08
T/W =6
Capacity for Gutter
equations:
Where:
Qs = Discharge within the Roadway
above the depressed section (cfs)
Qw = Discharge within the depressed
(gutter) section (cfs)
Cf = 0.56 for English units
Sx = Pavement cross slope (ft/ft)
Ts = Width of flow in the roadway above
depressed section
So = Gutter longitudinal slope (ft/ft)
Sw = Gutter depression cross slope (ft/ft)
T = Spread (ft)
W = Width of gutter depression (ft)
Capacity solution
Gutter Capacity - Drainage Basin 9 Gutter Capacity - Drainage Basin 10
So =0.0100 So =0.0100
Qs =2.33 cfs Qs =2.33 cfs
Eo =0.42 cfs Eo =0.42 cfs
Q =4.04 cfs Q =4.04 cfs
A=1.215 sf A=1.215 sf
V=3.33 ft/s V=3.33 ft/s
BASIN Gutter
Capacity (cfs)
25 Yr Design
Flow (cfs)
Capacity
greater than
25- yr flow?
9 4.04 1.97 Yes
10 4.04 1.89 Yes
Summary
Gutter Capacity Calculations
The gutter capacity is adequate for each drainage area.
Graf Street Apartments, Lot 2 of Minor Sub. 235
SWQQQ
QEQoW
0
S
E1
QQ
2
1
O3
8
S3
5
X
f
S STSn
CQ
1
8/3
XW
XWo
11T/W
/SS1
/SS1E
Gutter Section
Given:T =9.0 feet
W =1.50 feet
Ts =7.50 feet
Sw =0.0625 ft/ft
Sx =0.03 ft/ft
a =0.59 inches
d =3.24 inches
n =0.015
Where:
Qs =Discharge within the Roadway
above the depressed section (cfs)
Qw =Discharge within the depressed
(gutter) section (cfs)
Capacity for Inlets on Grade Cf =0.56 for English units
(Standard 24x36 Curb inlet)Sx =Pavement cross slope (ft/ft)
Ts =Width of flow in the roadway above
Drainage Basin 9 depressed section
So =Gutter longitudinal slope (ft/ft)
Qw =1.95 cfs Sw =Gutter depression cross slope (ft/ft)
Qs =2.66 cfs T =Spread (ft)
Cross-sectional area of flow W =Width of gutter depression (ft)
A =1.22 ft2
Gutter Velocity
V =3.79 ft/sec
Fraction of side flow intercepted
Rs =0.18
Total flow capacity intercepted by the inlet
Qint =2.51 cfs
Qbypass =2.10 cfs
Design Q for inlet #1
Q25 =1.97 cfs Single Inlet Sufficient
Drainage Basin 10
Qw =1.95 cfs
Qs =2.66 cfs
Cross-sectional area of flow
A =1.22 ft2
Gutter Velocity
V =3.79 ft/sec
Fraction of side flow intercepted
Rs =0.18
Total flow capacity intercepted by the inlet
Qint =2.51 cfs
Qbypass =2.10 cfs
Design Q for inlet #2
Q25 =1.89 cfs Single Inlet Sufficient
Inlet Capacity Calculations
Graf Street Apartments, Lot 2 of Minor Sub. 235
3130 Verona Avenue • Buford, GA 30518
(866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490
© Nyloplast Inlet Capacity Charts June 2012
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10
Ca
p
a
c
i
t
y
(
c
f
s
)
Head (ft)
Nyloplast 8" Drop In Grate Inlet Capacity Chart
Basin 9 & 10 Pipe Sizing
CIRCULAR CHANNEL
Manning's Eqn.1.486 A R2/3 S1/2
n
Diameter,do (in) =15.0
Diameter,do (ft) =1.25
Units =1.486
n =0.015
Slope, S (ft/ft)0.005
Depth, y (ft) Theta (rad) Area, A (ft2)
Wetted
Perimeter, P
(ft)
Hydraulic
Radius, R
(ft)
Top Width,
T (ft)
Hydraulic
Depth, D
(ft)
Section
Factor, Z
(ft5/2) Q (cfs) Q (gpm)
Q (gpd - 8
hour day) V (ft/s)
Energy, E
= V2/2g
(ft)
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.0 0.0 0.00
0.06 0.90 0.02 0.56 0.04 0.54 0.04 0.00 0.02 8.5 4095.3 0.8 0.01
0.13 1.29 0.06 0.80 0.08 0.75 0.09 0.02 0.08 37.1 17804.7 1.3 0.03
0.19 1.59 0.12 0.99 0.12 0.89 0.13 0.04 0.19 86.4 41454.3 1.7 0.04
0.25 1.85 0.17 1.16 0.15 1.00 0.17 0.07 0.35 155.6 74681.3 2.0 0.06
0.31 2.09 0.24 1.31 0.18 1.08 0.22 0.11 0.54 243.4 116818.8 2.3 0.08
0.38 2.32 0.31 1.45 0.21 1.15 0.27 0.16 0.78 347.9 167005.9 2.5 0.10
0.44 2.53 0.38 1.58 0.24 1.19 0.32 0.22 1.04 467.2 224236.5 2.7 0.11
0.50 2.74 0.46 1.71 0.27 1.22 0.37 0.28 1.33 598.7 287385.0 2.9 0.13
0.56 2.94 0.54 1.84 0.29 1.24 0.43 0.35 1.65 740.0 355218.7 3.1 0.15
0.63 3.14 0.61 1.96 0.31 1.25 0.49 0.43 1.98 888.3 426402.7 3.2 0.16
0.69 3.34 0.69 2.09 0.33 1.24 0.56 0.52 2.32 1040.6 499497.4 3.4 0.17
0.75 3.54 0.77 2.22 0.35 1.22 0.63 0.61 2.66 1193.6 572948.9 3.5 0.19
0.81 3.75 0.84 2.34 0.36 1.19 0.71 0.71 2.99 1343.9 645069.1 3.5 0.20
0.88 3.96 0.92 2.48 0.37 1.15 0.80 0.82 3.31 1487.5 714000.7 3.6 0.20
0.94 4.19 0.99 2.62 0.38 1.08 0.91 0.94 3.61 1620.1 777654.1 3.7 0.21
1.00 4.43 1.05 2.77 0.38 1.00 1.05 1.08 3.87 1736.6 833588.9 3.7 0.21
1.06 4.69 1.11 2.93 0.38 0.89 1.25 1.24 4.08 1830.8 878765.1 3.7 0.21
1.13 5.00 1.16 3.12 0.37 0.75 1.55 1.45 4.22 1893.6 908917.6 3.6 0.20
1.19 5.38 1.20 3.36 0.36 0.54 2.21 1.79 4.25 1909.1 916351.7 3.5 0.19
1.25 6.28 1.23 3.93 0.31 0.00 3.96 1777.3 853093.6 3.2 0.16
Basin 9 + 10 Q =3.86 cfs Capacity?OK
Q =
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40
Depth (ft)
Q (CFS)
V (ft/s)
E (ft)
y
do
T
THETA
Appendix C – Test Pit Location Map and
Infiltration Calculations
Project Name:Graf St. Apartments Test Number:1 (TP-01 on map)
Diameter of Test Hole:24"Depth of Test Hole:9.83 ft.
Date and Time Soak Period Began: 4/3/20 @ 9:00 am Ended: 4/3/20 @ 10:15 am
Date Test Began:4/3/2020
9.83 ft.
Test Results
Start Time
of Day
End Time
of Day
Time Interval
(Minutes)
Initial Distance
Below Reference
Point (ft.)
Final Distance
Below Reference
Point (ft.)
Drop in
Water
Level (in.)
Percolation Rate
(in/min)
0 1 1 8.01 8.20 2.28 2.28
1 2 1 8.20 8.37 2.04 2.04
2 3 1 8.37 8.49 1.44 1.44
0 1 1 8.02 8.20 2.16 2.16
1 2 1 8.20 8.34 1.68 1.68
2 3 1 8.48 8.48 1.68 1.68
Percolation Test Form
Distance of the reference point
above the bottom of the hole:
Project Name:Graf St. Apartments Test Number:2 (TP-51 on map)
Diameter of Test Hole:24"Depth of Test Hole:9.92 ft.
Date and Time Soak Period Began: 4/3/20 @ 10:40 am Ended: 4/3/20 @ 11:45 am
Date Test Began:4/3/2020
9.92 ft.
Test Results
Start Time
of Day
End Time
of Day
Time Interval
(Minutes)
Initial Distance
Below Reference
Point (ft.)
Final Distance
Below Reference
Point (ft.)
Drop in Water
Level (in.)
Percolation Rate
(in/min)
0 1 1 7.10 7.42 3.84 2.28
1 2 1 7.42 7.60 2.16 2.04
2 3 1 7.60 7.74 1.68 1.44
0 1 1 2.60 4.21 19.32 2.16
1 2 1 4.21 5.40 14.28 1.68
2 3 1 5.40 6.05 7.80 1.68
Test #1 Test #2 Test #3
Avg. Infiltration
Rate (in/min):
Avg. Infiltration
Rate w/ FS = 2:
Infiltration Rate (in/min):2.28 2.16 3.84 2.76 1.38
*Did not use infiltration rate of 19.32 in/min as this was an outlier.
Percolation Test Form
Distance of the reference point
above the bottom of the hole:
Appendix D – Groundwater Monitoring Data
and Geotech Report Figures
REVISION
F
I
G
U
R
E
D
E
S
I
G
N
E
D
B
Y
:
Q
U
A
L
I
T
Y
C
H
E
C
K
:
J
O
B
N
O
.
F
I
E
L
D
B
O
O
K
D
R
A
W
N
B
Y
:
D
A
T
E
:
B
1
9
-
0
1
4
B
O
R
I
N
G
M
A
P
REV DATE
N
O
T
F
O
R
C
O
N
S
T
R
U
C
T
I
O
N
GRAF STREET APARTMENTS
BOZEMAN, MONTANA
TEST PIT LOCATION MAP B
1
9
-
0
1
4
3
.
5
.
1
9
.
D
W
G
1
D
S
O
Engineering
tdhengineering.com
TEST PIT AND GROUND WATER DATA
FIGURE
DESIGNED BY:
QUALITY CHECK:
JOB NO.
FIELDBOOK
DRAWN BY: BJL
DATE:
B19-014
3.8.19
GR
A
F
S
T
R
E
E
T
A
P
A
R
T
M
E
N
T
S
BO
Z
E
M
A
N
,
M
O
N
T
A
N
A
RE
V
D
A
T
E
RE
V
I
S
I
O
N
NOT
F
O
R
CONS
T
R
U
C
T
I
O
N
En
g
i
n
e
e
r
i
n
g
td
h
e
n
g
i
n
e
e
r
i
n
g
.
c
o
m
B19-014 FIGURE 2
SU
M
M
A
R
Y
O
F
T
E
S
T
P
I
T
S
A
N
D
G
R
O
U
N
D
W
A
T
E
R
M
O
N
I
T
O
R
I
N
G
.DWG
2
Graf St. Apartments
Groundwater Monitoring Summary *Measure from T.O.P.*
Measured GW Measured GW Measured GW Measured GW
1 4966.35 2.00 4964.35 7.37 4958.98 7.57 4958.78 7.94 4958.41 7.73 4958.62
2 4970.85 1.50 4969.35 7.15 4963.70 7.25 4963.60 7.50 4963.35
3 4977.13 0.00 4977.13 4.65 4972.48 4.67 4972.46 4.85 4972.28
4 4981.20 2.50 4978.70 8.99 4972.21 9.08 4972.12 9.18 4972.02 9.14 4972.06
Measured GW Measured GW Measured GW Measured GW
1 4966.35 2.00 4964.35 6.54 4959.81 6.17 4960.18 6.64 4959.71 6.55 4959.80
2 4970.85 1.50 4969.35 7.48 4963.37 7.43 4963.42 7.39 4963.46 7.50 4963.35
3 4977.13 0.00 4977.13 4.80 4972.33 4.62 4972.51 4.64 4972.49 4.58 4972.55
4 4981.20 2.50 4978.70 8.95 4972.25 8.72 4972.48 8.91 4972.29 8.80 4972.40
Measured GW Measured GW Measured GW Measured GW
1 4966.35 2.00 4964.35 7.81 4958.54 6.76 4959.59 6.52 4959.83
2 4970.85 1.50 4969.35 7.61 4963.24 6.82 4964.03 7.06 4963.79
3 4977.13 0.00 4977.13 4.89 4972.24 4.64 4972.49 4.77 4972.36
4 4981.20 2.50 4978.70 9.12 4972.08 9.06 4972.14 9.02 4972.18
Well 1 Well 2 Well 3 Well 4 Well 1 Well 2 Well 3 Well 4
5/8/2020 4958.98 4972.21 5.37 6.49
5/15/2020 4958.78 4963.70 4972.48 4972.12 5.57 5.65 4.65 6.58
5/27/2020 4958.41 4963.60 4972.46 4972.02 5.94 5.75 4.67 6.68
6/5/2020 4958.62 4963.35 4972.28 4972.06 5.73 6.00 4.85 6.64
6/12/2020 4959.81 4963.37 4972.33 4972.25 4.54 5.98 4.80 6.45
6/19/2020 4960.18 4963.42 4972.51 4972.48 4.17 5.93 4.62 6.22
6/26/2020 4959.71 4963.46 4972.49 4972.29 4.64 5.89 4.64 6.41
7/3/2020 4959.80 4963.35 4972.55 4972.40 4.55 6.00 4.58 6.30
7/13/2020 4958.54 4963.24 4972.24 4972.08 5.81 6.11 4.89 6.62
7/20/2020 4959.59 4964.03 4972.49 4972.14 4.76 5.32 4.64 6.56
7/27/2020 4959.83 4963.79 4972.36 4972.18 4.52 5.56 4.77 6.52
Min 4.17 5.32 4.58 6.22
Max 5.94 6.11 4.89 6.68
Groundwater Elevation (ft) Groundwater Depth (ft)
Groundwater Depths Summary
Date
5/15/2020 5/27/2020 6/5/2020
Monitoring Well
Top of Pipe
Elevation
Top of Casing
to Ground (ft)
Grnd Elevation
@ Pipe Base
5/8/2020
6/19/2020 6/26/2020 7/3/2020
Monitoring Well
Top of Pipe
Elevation
Top of Casing
to Ground (ft)
Grnd Elevation
@ Pipe Base
7/13/2020 7/20/2020 7/27/2020
Monitoring Well
Top of Pipe
Elevation
Top of Casing
to Ground (ft)
Grnd Elevation
@ Pipe Base
6/12/2020
Appendix E – Detention and Retention
Calculations
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 1
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)160,623
total area:3.69 acres
composite C:0.71
Infiltration Calculation
Width of Paver =9 ft
Length of Pavers =145.00 ft
Infiltration Surface Area = 1,305 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =2.50 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 23.99 1439 150 1289
3 4.49 11.74 2114 450 1664
5 3.22 8.43 2528 750 1777
7 2.59 6.77 2844 1051 1793
9 2.20 5.75 3105 1351 1755
11 1.93 5.05 3331 1651 1680
13 1.73 4.53 3532 1951 1581
15 1.58 4.13 3713 2251 1462
17 1.45 3.80 3879 2551 1328
19 1.35 3.54 4033 2851 1182
21 1.27 3.32 4177 3152 1026
23 1.19 3.12 4312 3452 861
25 1.13 2.96 4440 3752 688
27 1.08 2.82 4561 4052 509
29 1.03 2.69 4677 4352 325
31 0.98 2.57 4787 4652 135
required detention storage (ft3) =1,793
Storage Volume Calculation
Width of Basin =9 ft
Length of Basin =145 ft
Depth of Basin =3.5 ft *Excludes 6" thick Pavers
Gross Basin Volume = 4,568 ft3
Volume (40% voids) =1,827 ft3
Top of Paver Elevation 4,965.68 ft
High Groundwater Elev.4,961.25 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,961.68 ft seasonal high groundwater data
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 2
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)15,581
total area:0.36 acres
composite C:0.71
Infiltration Calculation
Width of Paver =10 ft
Length of Pavers =15.00 ft
Infiltration Surface Area = 150 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =0.29 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 2.33 140 17 122
3 4.49 1.14 205 52 153
5 3.22 0.82 245 86 159
7 2.59 0.66 276 121 155
9 2.20 0.56 301 155 146
11 1.93 0.49 323 190 133
13 1.73 0.44 343 224 118
15 1.58 0.40 360 259 101
17 1.45 0.37 376 293 83
19 1.35 0.34 391 328 64
21 1.27 0.32 405 362 43
23 1.19 0.30 418 397 22
25 1.13 0.29 431 431 -1
27 1.08 0.27 442 466 -23
29 1.03 0.26 454 500 -47
31 0.98 0.25 464 535 -70
required detention storage (ft3) =159
Storage Volume Calculation
Width of Basin =10 ft
Length of Basin =15 ft
Depth of Basin =3.5 ft *Excludes 6" thick Pavers
Gross Basin Volume = 525 ft3
Volume (40% voids) =210 ft3
Top of Paver Elevation 4,968.26 ft
High Groundwater Elev.4,961.00 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,964.26 ft seasonal high groundwater data
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 3
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)51,818
total area:1.19 acres
composite C:0.71
Infiltration Calculation
Width of Paver =8 ft
Length of Pavers =54.00 ft
Infiltration Surface Area = 432 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =0.83 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 7.74 464 50 415
3 4.49 3.79 682 149 533
5 3.22 2.72 815 248 567
7 2.59 2.18 917 348 570
9 2.20 1.86 1002 447 555
11 1.93 1.63 1075 546 528
13 1.73 1.46 1139 646 494
15 1.58 1.33 1198 745 453
17 1.45 1.23 1252 845 407
19 1.35 1.14 1301 944 357
21 1.27 1.07 1348 1043 304
23 1.19 1.01 1391 1143 249
25 1.13 0.95 1432 1242 190
27 1.08 0.91 1471 1341 130
29 1.03 0.87 1509 1441 68
required detention storage (ft3) =570
Storage Volume Calculation
Width of Basin =8 ft
Length of Basin =54 ft
Depth of Basin =3.5 ft *Excludes 6" thick Pavers
Gross Basin Volume = 1,512 ft3
Volume (40% voids) =605 ft3
Top of Paver Elevation 4,968.77 ft
High Groundwater Elev.4,964.50 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,964.77 ft seasonal high groundwater data
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 4
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)48,789
total area:1.12 acres
composite C:0.71
Infiltration Calculation
Width of Paver =15 ft
Length of Pavers =38 ft
Infiltration Surface Area = 570 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =1.09 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 7.29 437 66 372
3 4.49 3.57 642 197 445
5 3.22 2.56 768 328 440
7 2.59 2.06 864 459 405
9 2.20 1.75 943 590 353
11 1.93 1.53 1012 721 291
13 1.73 1.38 1073 852 221
15 1.58 1.25 1128 983 145
17 1.45 1.16 1178 1114 64
19 1.35 1.07 1225 1245 -20
21 1.27 1.01 1269 1377 -108
23 1.19 0.95 1310 1508 -198
25 1.13 0.90 1349 1639 -290
27 1.08 0.86 1385 1770 -384
29 1.03 0.82 1421 1901 -480
31 0.98 0.78 1454 2032 -578
required detention storage (ft3) =445
Storage Volume Calculation
Width of Basin =15 ft
Length of Basin =38 ft
Depth of Basin =2.0 ft *Excludes 6" thick Pavers
Gross Basin Volume = 1,140 ft3
Volume (40% voids) =456 ft3
Top of Paver Elevation 4,970.24 ft
High Groundwater Elev.4,967.50 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,967.74 ft seasonal high groundwater data
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 5
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)183,041
total area:4.20 acres
composite C:0.71
Infiltration Calculation
Width of Paver =30 ft
Length of Pavers =50.00 ft
Infiltration Surface Area = 1,500 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =2.88 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 27.33 1640 173 1468
3 4.49 13.38 2409 518 1892
5 3.22 9.60 2881 863 2018
7 2.59 7.72 3241 1208 2033
9 2.20 6.55 3539 1553 1986
11 1.93 5.75 3796 1898 1899
13 1.73 5.16 4025 2243 1782
15 1.58 4.70 4231 2588 1644
17 1.45 4.33 4421 2933 1488
19 1.35 4.03 4596 3278 1319
21 1.27 3.78 4760 3623 1138
23 1.19 3.56 4914 3968 947
25 1.13 3.37 5060 4313 747
27 1.08 3.21 5198 4658 540
29 1.03 3.06 5330 5003 327
required detention storage (ft3) =2,033
Storage Volume Calculation
Width of Basin =30 ft
Length of Basin =50 ft
Depth of Basin =3.5 ft *Excludes 6" thick Pavers
Gross Basin Volume = 5,250 ft3
Volume (40% voids) =2,100 ft3
Top of Paver Elevation 4,974.24 ft
High Groundwater Elev.4,967.75 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,970.24 ft seasonal high groundwater data
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 6
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)126,106
total area:2.89 acres
composite C:0.71
Infiltration Calculation
Width of Paver =32 ft
Length of Pavers =36.00 ft
Infiltration Surface Area = 1,152 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =2.21 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 18.83 1130 132 997
3 4.49 9.22 1660 397 1262
5 3.22 6.62 1985 662 1322
7 2.59 5.32 2233 927 1305
9 2.20 4.51 2438 1192 1246
11 1.93 3.96 2615 1457 1158
13 1.73 3.55 2773 1722 1051
15 1.58 3.24 2915 1987 928
17 1.45 2.99 3046 2252 794
19 1.35 2.78 3167 2517 650
21 1.27 2.60 3280 2782 497
23 1.19 2.45 3386 3047 339
25 1.13 2.32 3486 3312 174
27 1.08 2.21 3581 3577 4
29 1.03 2.11 3672 3842 -170
required detention storage (ft3) =1,322
Storage Volume Calculation
Width of Basin =32 ft
Length of Basin =36 ft
Depth of Basin =3.0 ft *Excludes 6" thick Pavers
Gross Basin Volume = 3,456 ft3
Volume (40% voids) =1,382 ft3
Top of Paver Elevation 4,972.84 ft
High Groundwater Elev.4,969.00 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,969.34 ft seasonal high groundwater data
2131 Graf
Gravel Infiltration System
Stormwater Detention Basin Calculation
Basin 7
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)82,565
total area:1.90 acres
composite C:0.71
Infiltration Calculation
Area of Grave infiltration swale 616 ft
Infiltration Surface Area = 616 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =1.18 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 12.33 740 71 669
3 4.49 6.04 1087 213 874
5 3.22 4.33 1299 354 945
7 2.59 3.48 1462 496 966
9 2.20 2.96 1596 638 959
11 1.93 2.59 1712 779 933
13 1.73 2.33 1815 921 894
15 1.58 2.12 1909 1063 846
17 1.45 1.96 1994 1204 790
19 1.35 1.82 2073 1346 727
21 1.27 1.70 2147 1488 660
23 1.19 1.61 2217 1629 587
25 1.13 1.52 2282 1771 511
27 1.08 1.45 2345 1913 432
29 1.03 1.38 2404 2054 350
required detention storage (ft3) =966
Storage Volume Calculation
Area of Gravel Infiltration =616 ft
Depth of Basin =4.0 ft
Gross Basin Volume = 2,464 ft3
Volume (40% voids) =986 ft3
Top of Storage Elevation 4,965.00 ft
High Groundwater Elev.4,961.00 ft *Estimated by a groundwater surface generated from monitored
Bottom of Storage Elev 4,961.00 ft seasonal high groundwater data
2131 Graf
Pervious Paver Detention System
Stormwater Detention Basin Calculation
Basin 8
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)17,555
total area:0.40 acres
composite C:0.71
Infiltration Calculation
Area of Permeable Pavers 154 ft
Infiltration Surface Area = 154 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =0.30 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 2.62 157 18 140
3 4.49 1.28 231 53 178
5 3.22 0.92 276 89 188
7 2.59 0.74 311 124 187
9 2.20 0.63 339 159 180
11 1.93 0.55 364 195 169
13 1.73 0.49 386 230 156
15 1.58 0.45 406 266 140
17 1.45 0.42 424 301 123
19 1.35 0.39 441 336 104
21 1.27 0.36 457 372 85
23 1.19 0.34 471 407 64
25 1.13 0.32 485 443 43
27 1.08 0.31 499 478 20
29 1.03 0.29 511 514 -2
required detention storage (ft3) =188
Storage Volume Calculation
Area of Pavers =154 ft
Depth of Basin =3.5 ft *Excludes 6" thick Pavers
Gross Basin Volume = 539 ft3
Volume (40% voids) =216 ft3
Top of Paver Elevation 4,976.50 ft
High Groundwater Elev.4,968.00 ft *Estimated by a groundwater surface generated from monitored
Bottom of Detention Elev 4,972.50 ft seasonal high groundwater data
2131 Graf 8/10/2020
Stormwater Retention Basin Calculation
Basins 9 & 10
Calculation of Required Volume for Underground Storm Water Retention System
Areas (ft2):Total: 130,752
total area: 3.00 acres
composite C: 0.71
Required Retention Pond Calculations:
Q = CIA
C = 0.71 (post-development)
I = 0.41 in/hr (Figure I-3, Pg 32, 10-yr, 2-hr storm)
A = 3.00 acres
Q =0.87 cfs
required retention storage (ft3) =6,291 ft3
Contech Corrugated CMP Pipe Storage Calculations
Pipe Area
A = 3.14 x R2
Diameter Radius
3 1.5 3.14 = 7.07 ft2
Pipe Volume
A = 3.14 x R2
Diameter Radius
3 1.5 3.14 = 7.07 ft2
Length (6-rows @ 70' each)=420 ft
Volume = 2,967 ft3
Stone Volume
Stone Width = 5.5 ft
Stone Depth = 5 ft
Area = 27.5 ft2
Less Pipe Area = 7.07 ft2
Stone Area = 20.44 ft2
Pipe Length =420 ft
Storage Volume in Stone (40% voids)=3,433 ft3
Total Storage Volume =6,400 ft3
Bottom of Storage Elevation = 4,963.0 ft
Seasonal High Groundwater Elevation = 4,962.5 ft
0.5" Rainfall Required Retention Calculations
Area 130,752 sf
Rainfall 0.5 inches
0.042 ft
Volume to be Retained 5,448 cf 10-yr 2-hr Storm Controls
Retention Calc.xls
2131 Graf
Gravel Infiltration System
Stormwater Detention Basin Calculation
Basin 11
Calculation of Required Volume for Storm Water Infitration System
Design Rainfall Freq.10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Post-development Calculations
Basin Area (ft2)22,915
total area:0.53 acres
composite C:0.71
Infiltration Calculation
Area of Gravel Swale 180 ft
Infiltration Surface Area = 180 ft2
Infitration Rate =1.38 inch/min 1/2 of field measurement
0.00192 f/s Infiltration Rate
Volumetric Infiltration Rate =0.35 cfs
Storm Duration Intensity Future Runoff Runoff Release Required
(minutes)(in/hr)Rate (cfs)Volume (cf)Volume (cf)Storage (cf)
1 9.16 3.42 205 21 185
3 4.49 1.68 302 62 239
5 3.22 1.20 361 104 257
7 2.59 0.97 406 145 261
9 2.20 0.82 443 186 257
11 1.93 0.72 475 228 248
13 1.73 0.65 504 269 235
15 1.58 0.59 530 311 219
17 1.45 0.54 553 352 202
19 1.35 0.50 575 393 182
21 1.27 0.47 596 435 161
23 1.19 0.45 615 476 139
25 1.13 0.42 633 518 116
27 1.08 0.40 651 559 92
29 1.03 0.38 667 600 67
required detention storage (ft3) =261
Storage Volume Calculation
Area of Pavers =180 ft
Depth of Basin =4.0 ft
Gross Basin Volume = 720 ft3
Volume (40% voids) =288 ft3
Top of Storage Elevation 4,966.00 ft
High Groundwater Elev.4,960.00 ft *Estimated by a groundwater surface generated from monitored
Bottom of Storage Elev 4,962.00 ft seasonal high groundwater data
Appendix F – Stormwater Maintenance Plan
STORMWATER MAINTENANCE PLAN
2131 Graf
The recommended stormwater facility maintenance is displayed below. It is the Property
Owner’s Associations responsibility for routine inspection and maintenance of the following
items:
1. Keep the sidewalk chases, curb & gutter, and swales free of leaves, litter, and other debris.
2. Keep the inlets of the facilities free of leaves, rocks, and other debris.
3. Quarterly inspect and clean curb inlets and pipes.
4. Remove sediment from the curb inlet sumps located on S 21st Ave by hand during the
summer months whenever sediment has accumulated to greater than 9” in the bottom of the
basin, refer to sheet C1.5 included in the stormwater report for location of curb inlets.
5. The Permeable Paver infiltration systems are to be inspected and maintained per the
attached Powerblock Permeable Pavement System Guide Construction Specification, Part 4
- Inspection and Maintenance, or approved equivalent. The Permeable Paver infiltration
systems are displayed on Sheets C1.5 & C1.6 and corresponding Basins are shown on sheet
SD1.1, included in the stormwater report.
6. The Area Drain Inlets and Perforated Pipe with Drain Rock infiltration systems are to be
maintained by the owner. The area drains should be inspected quarterly and kept free from
debris, leaves, litter, and other debris. The perforated pipe should be inspected yearly and
sediment should be removed from the pipes if necessary. The infiltration systems are
displayed on sheets C1.5 & C1.6 and corresponding Basins are shown on sheet SD1.1,
included in the stormwater report.
6. The buried retention systems are displayed on Sheet C1.5 of the stormwater report. The
buried retention system maintenance is as follows:
Minimum required maintenance includes a quarterly inspection during the first year
of operation and a yearly inspection thereafter. Utilize inspection ports for
inspections.
The inspection ports can be used to pump water into the system and re-
suspend accumulated sediment so that is may be pumped out. Flush and pump as
inspections deem necessary.
7. Waste shall be disposed of from maintenance of facilities in accordance with applicable
federal, state and local laws and regulations.
8. Property Owner’s Association to maintain and fund Operation and Maintenance of
facilities.
_______________________________
Property Owners Association
PowerBlock® Permeable Pavement System
Guide Construction Specification
PART 1 GENERAL
1. Related Documents
A. Drawings, technical specifications, and general provisions of the Contract as
modified herein apply to this section.
2. Description of the Work Included
A. Provide excavation and base preparation per geotechnical engineer's
recommendations and/or as shown on the design drawings.
B. Provide and install PowerBlock® and all related products including base materials,
geotextiles, and geogrids per the manufacturer’s installation guidelines provided in
this section.
C. Perform post-installation testing.
D. Protect PowerBlock® system from contamination due to construction traffic and
construction sedimentation after installation until the site is completely stabilized.
3. Quality Assurance
A. Installation Contractor shall demonstrate the following experience:
1. A minimum of three permeable pavement projects completed within the last
2 years of a similar or larger size and complexity.
2. A minimum of 25,000 square feet of permeable pavement installed within the
last 2 years.
3. Installation Contractor experience requirement may be waived if the
manufacturer’s representative provides on-site training and review during
construction.
B. Installation Personnel: Performed only by skilled workers with a satisfactory record
of performance on permeable pavement construction projects of comparable size and
complexity.
C. Contractor must have the manufacturer’s representative available for site review if
requested by the Owner.
4. Submittals
A. Submit proposed PowerBlock® layout drawings.
B. Submit manufacturer’s product data, including all requirements detailed in this
specification.
C. Submit material specifications for all geotextiles and geogrids.
D. Submit material specification for base stone and aggregates.
E. Any proposed equal alternative product substitution to this specification must be
submitted for review and approved prior to the bid opening. The review package
should include third party performance data that meets or exceeds the criteria in
Table 2.1A.
5. Storage and Handling
A. Protect concrete pavers during shipment, storage, and installation against staining,
chipping, cracking, and other damage.
B. Coordinate delivery and paving schedule with other construction activities.
6. Preinstallation Conference
A. Prior to the start of the installation, a preinstallation conference shall occur with
Owner representatives, the general contractor, the installation contractor, and the
manufacturer’s representative.
B. Coordinate installation for the PowerBlock® system with other on-site activities to
minimize sedimentation and contamination of the permeable pavement during
construction. All non-installation related construction traffic, particularly equipment
used for earthwork, should be routed around the permeable pavement. Stabilize
denuded soils contributing runoff to the permeable pavement prior to
commissioning the system.
PART 2: PRODUCTS
1. Permeable Paver
A. Permeable pavement shall be constructed from pre-manufactured, interlocking
concrete blocks that do not require stone or sand filler between the blocks, leaving
the joints open to allow rapid infiltration of runoff through the joints. The blocks and
completed permeable pavement shall meet the following properties:
Table 2.1A
PROPERTY DESCRIPTION VALUE
Dimensions Length x Width x Height 11.75” x 13.70” x 4.5” (+/-
1/8”)
Block Weight Pounds 44 lbs Minimum
Loading Capability Traffic Rating HS-20 / HS-25
Open Joint Width Inches 0.25” (+/- 0.02”)
Joint Filler Between Blocks Material Used NONE ALLOWED1
Post-Installation, Field-
Verified Surface Infiltration
Rate3
ASTM C-1701 / C-1701-M09
/ ASTM C-1781 / C-140
1,000 inches / hour average
(Minimum 3 tests)
Compressive Strength ASTM D-6684 / C-140 4,000 psi (average)
3,500 psi (minimum)
Freeze / Thaw Resistance2 ASTM C-67 / C-1645 / C-936 COMPLIANT
Abrasion Resistance2 C-4182 COMPLIANT
NOTE 1: No filler material is allowed to be used between the blocks. Use ONLY blocks that do not
require stabilizing stone/sand between the units.
NOTE 2: Testing by the National Concrete Masonry Association (NCMA) will be made available for
freeze/thaw and abrasion resistance upon request.
NOTE 3: The completed permeable pavement system must be tested in-situ after installation and will
only be accepted when required performance value shown in Table 2.1A has been documented
by a third party. Final test report must be submitted to the Owner prior to acceptance.
B. Visual Inspection
1. All blocks shall be sound and free of defects that would interfere with the
proper placing of the units or impair the strength or performance of the
permeable pavement system.
2. Surface cracks incidental to the usual methods of manufacture, or surface
chipping resulting from customary methods of handling in shipment and
delivery, shall not be deemed grounds for rejection.
3. Cracks exceeding 0.25 inches in width and/or 1.0 inches in depth or larger
shall be deemed grounds for rejection.
4. Ensure the PowerBlock delivered to the site matches the color requirements
on plans.
C. The permeable paver shall be PowerBlock® or pre-approved equal (as noted in Part
1, Section 4.E), as represented and distributed by:
ACF Environmental
PH. (800) 448-3636
info@acfenv.com
acfenvironmental.com
D. When PowerBlock® installation may be exposed to de-icing salts or salt air in coastal
climates, blocks should be sealed after installation with optional Prossoco Saltguard
WB or equivalent. If specified, the coating shall be applied per manufacturer’s
recommendations.
2. Stone Base
A. Permeable pavements require site specific design based on both structural and
hydrologic requirements of the pavement. Depths shown on typical drawings must
be evaluated and modified as necessary by the engineer of record.
B. All aggregate shall be clean and angular on all sides, with no less than 90% fractured
faces. Do not use rounded river gravel or fractured river gravel for any application.
C. If more than 6” of base stone is required, use AASHTO #2 Stone or simillar for the
lower layers.
ASTM No. 2 Subbase
Grading Requirements
Sieve Size Percent Passing
75 mm (3 in.) 100
63 mm (2 1/2 in.) 90 to 100
50 mm (2 in.) 35 to 70
37.5 mm (1 1/2 in.) 0 to 15
19 mm (3/4 in.) 0 to 5
D. AASHTO #57 Stone shall be used as a leveling course for the upper 4” to 6” of the
base layer.
ASTM No. 57 Base
Grading Requirements
Sieve Size Percent Passing
37.5 mm (1 1/2 in.) 100
25 mm (1 in.) 95 to 100
12.5 mm (1/2 in.) 25 to 60
4.75 mm (No. 4) 0 to 10
2.36 mm (No. 8) 0 to 5
3. Geotextiles
A. Use a woven monofilament geotextile, such as ACF M200, or as specified in the
contract documents.
4. Edge Restraint
A. Perimeter: Edges of the PowerBlock area shall be finished with a Standing Curb
with a vertical face, or as shown on plans
B. Internal Edges: Edges of the PowerBlock area where traffic access is required shall
be finished with a flush Ribbon Curb, or as shown on plans.
PART 3: FOUNDATION PREPARATION AND BLOCK INSTALLATION
1. Foundation & Preparation
A. Prepare subgrade as noted on plans. Typically, compaction of underlying subgrade
soil should be avoided or minimized in order to encourage infiltration of stormwater.
Subgrade should be uniform, level, and free of lumps and debris. All questions about
the adequacy of the subgrade should be directed to the owner’s engineer, who will
approve the subgrade conditions prior to placement of the stone base.
B. Place a woven monofilament geotextile, such as ACF M200, on the subgrade base
and sides of the excavation to prevent contamination of the clean aggregate base or
as specified in the contract documents. Overlap seams a minimum of 12” in all
directions, or as shown on plans.
C. Install base materials in layers uniformly spread and compacted in 6” – 8” lifts or as
noted on plans. When final layer of base stone is installed, compact first with a roller
and finish with a 10,000 psi plate compactor in both the perpendicular and parallel
directions. Compaction is complete when no movement of base materials is
observed. Base shall be a smooth, plane surface, firm and non-yielding prior to
placement of the PowerBlock®.
D. Confirm finished elevations of the base match plan requirements.
E. Completed base shall be proof rolled and inspected and approved by engineer or
record. Reconstruct areas where deflection exceeds acceptable limits as determined
by engineer.
2. Pavers
A. Ensure PowerBlock® units are free of foreign material before installation.
B. Set PowerBlock® pavers as shown on plans, within the specified lines and grades
shown on plans. Units shall be installed straight and true to the required lines. Ensure
joint widths are consistent throughout installation.
1. Installation shall proceed by adding blocks adjacent to previously installed
units.
2. On sloped areas, work from lower areas toward the higher elevations.
C. Cut PowerBlock® units as needed to accommodate field conditions and to achieve a
consistent pattern.
D. When a substantial area of PowerBlock® units has been installed, the pavers shall be
static rolled to ensure a consistent top elevation.
E. Replace pavers that are broken, substantially chipped, or stained during construction.
F. The joints between the blocks shall not be backfilled with smaller aggregates or sand
in order to function properly. The joints shall be left open at all times, including
following maintenance of the permeable pavement.
G. Within 60 days of completion of the installation, the surface infiltration rate of the
pavement shall be field verified to confirm the required infiltration rate of the
pavement (per Table 2.1A). If the system fails to perform as required, it shall be
removed and replaced at no cost to the Owner.
PART 4: INSPECTION AND MAINTENANCE
1. Inspection
A. Inspect the permeable pavement, noting areas of standing water or significant
accumulation of joint debris.
B. If joints are excessively filled with debris or sediment, a surface infiltration test may
be performed per Table 2.1A to determine the capabilities of the system.
2. Maintenance
A. Maintenance shall be performed when either:
1. The surface infiltration rates of more than 75% of the surface area fall below
10% of the rate required per Table 2.1A.
2. Surface ponding remains for 24 hours in an area larger than 10 square feet.
3. Other desired maintenance at the Owner’s discretion to optomize
performance.
B. Maintenance shall be performed with a vacuum device, not a mechanical sweeper, to
remove accumulated debris from joints. This may be accomplished with smaller
hand-held devices or with vacuum trucks such as the Elgin Whirlwind. Adjust device
settings to avoid movement or lifting of block, or removal of the base stone
underneath the blocks at all times.